1. Technical Field
The present disclosure relates to an off-axis optical system.
2. Description of Related Art
Compared with conventional rotationally symmetric surfaces, freeform surfaces have asymmetric surfaces and more degrees of freedom in design, which can reduce aberrations and simplify the structure of the reflective system. Thus, freeform surfaces are often used in off-axis three-mirror optical systems.
However, the mirrors in conventional off-axis three-mirror system are mostly spherical or aspheric surfaces. There are more factors, such as volume, weight, and the number of lenses, to be considered during the designing process; it is difficult to design off-axis three-mirror optical systems with simple structure and excellent imaging. In addition, conventional off-axis three-mirror optical systems with spherical surfaces or aspherical surfaces make it difficult to achieve multiple fields imaging with large field of view (FOV), such as more than 60°.